 section .data
    input_string db 'bab', 0     ; Input string to check for palindrome
    msg_palindrome db 'Palindrome', 0
    msg_not_palindrome db 'Not Palindrome', 0

section .bss
    reversed_string resb 20          ; Space to store the reversed string

section .text
    global _start

_start:
    ; Calculate the length of the input string
    mov ecx, 0                      ; Initialize counter for string length
calculate_length:
    cmp byte [input_string + ecx], 0  ; Check if end of string
    je reverse_string                ; If end of string, proceed to reversing
    inc ecx                         ; Increment counter
    jmp calculate_length            ; Continue calculating length

reverse_string:
    ; Reverse the input string
    mov esi, 0                      ; Source index (starting from beginning of input string)
    mov edi, ecx                    ; Destination index (starting from end of input string)
    dec edi                         ; Adjust destination index to end of input string

reverse_loop:
    cmp esi, edi                    ; Check if source index crosses destination index
    jge compare_strings             ; If so, proceed to comparing strings

    mov al, [input_string + esi]   ; Load byte from input string
    mov [reversed_string + edi], al ; Store byte to reversed string
    inc esi                         ; Increment source index
    dec edi                         ; Decrement destination index
    jmp reverse_loop                ; Continue loop

compare_strings:
    ; Compare the original and reversed strings
    mov esi, input_string           ; Point esi to original string
    mov edi, reversed_string        ; Point edi to reversed string

compare_loop:
    cmp byte [esi], 0               ; Check if end of string
    je is_palindrome                ; If end of string, strings are identical (palindrome)
    cmpsb                           ; Compare bytes at esi and edi
    jne not_palindrome              ; If bytes are not equal, strings are not identical

is_palindrome:
    ; Output message indicating that the string is a palindrome
    mov eax, 4                      ; syscall number for sys_write
    mov ebx, 1                      ; file descriptor 1 (stdout)
    mov ecx, msg_palindrome         ; pointer to the message
    mov edx, 10                     ; length of the message
    int 0x80                        ; call the kernel
    jmp exit_program                ; Exit the program

not_palindrome:
    ; Output message indicating that the string is not a palindrome
    mov eax, 4                      ; syscall number for sys_write
    mov ebx, 1                      ; file descriptor 1 (stdout)
    mov ecx, msg_not_palindrome     ; pointer to the message
    mov edx, 14                     ; length of the message
    int 0x80                        ; call the kernel

exit_program:
    ; Exit the program
    mov eax, 1                      ; syscall number for sys_exit
    xor ebx, ebx                    ; exit code 0
    int 0x80                        ; call the kernel

created 1 year ago

Assembly Online Compiler

Write, Run & Share Assembly code online using OneCompiler's Assembly online compiler for free. It's one of the robust, feature-rich online compilers for Assembly language. Getting started with the OneCompiler's Assembly compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as Assembly and start coding.

About Assembly

Assembly language(asm) is a low-level programming language, where the language instructions will be more similar to machine code instructions.

Every assembler may have it's own assembly language designed for a specific computers or an operating system.

Assembly language requires less execution time and memory. It is more helful for direct hardware manipulation, real-time critical applications. It is used in device drivers, low-level embedded systems etc.

Syntax help

Assembly language usually consists of three sections,

Data section

To initialize variables and constants, buffer size these values doesn't change at runtime.
bss section

To declare variables
text section

_start specifies the starting of this section where the actually code is written.

Variables

There are various define directives to allocate space for variables for both initialized and uninitialized data.

1. To allocate storage space to Initialized data

Syntax

variable-name    define-directive    initial-value

Define Directive	Description	Allocated Space
DB	Define Byte	1 byte
DW	Define Word	2 bytes
DD	Define Doubleword	4 bytes
DQ	Define Quadword	8 bytes
DT	Define Ten Bytes	10 bytes

2. To allocate storage space to un-initialized data

Define Directive	Description
RESB	Reserve a Byte
RESW	Reserve a Word
RESD	Reserve a Doubleword
RESQ	Reserve a Quadword
REST	Reserve a Ten Bytes

Constants

Constants can be defined using

1. equ

To define numeric constants

CONSTANT_NAME EQU regular-exp or value

2. %assign

To define numeric constants.

%assign constant_name value

3. %define

To define numeric or string constants.

%define constant_name value

Loops

Loops are used to iterate a set of statements for a specific number of times.

mov ECX,n
L1:
;<loop body>
loop L1

where n specifies the no of times loops should iterate.

Procedures

Procedure is a sub-routine which contains set of statements. Usually procedures are written when multiple calls are required to same set of statements which increases re-usuability and modularity.

procedure_name:
   ;procedure body
   ret